GB2112541A

GB2112541A - Liquid crystal display panel and production method thereof

Info

Publication number: GB2112541A
Application number: GB08236379A
Authority: GB
Inventors: Seikichi Tanno; Koo Honjuyo; Hiroshi Suzuki; Tatsuo Igawa; Ren Ito; Fumio Nakano; Takao Miyashita; Yuzuru Shimazaki; Takao Umeda
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1981-12-25
Filing date: 1982-12-22
Publication date: 1983-07-20
Also published as: DE3248137A1; DE3248137C2; GB2112541B

Abstract

The interior surfaces of organic polymer film substrates 7a, 7b of liquid crystal displays 21 are chemically treated with a strong alkali or acid and organic polymer layers 16a, 16b are then deposited over all or part of these surfaces. An organic polymer layer may constitute an orientation controlling film (fig. 11), or may be overlain by transparent conductive layers 13 and an orientation controlling film 22a, 22b. The peripheral areas of the substrate are bonded together with an adhesive 18, and the films 16 may not extend over the bonding areas (16a, 16b in fig. 20) in which case the adhesive 18 extends to the substrates 7a, 7b. The arrangement permits improved bonding strength between the substrates without any sacrifice of transparency. <IMAGE>

Description

SPECIFICATION Liquid crystal display panel and production method thereof This invention relates to a liquid crystal display panel using organic polymer films as the substrates.

More particularly, the present invention relates to a liquid crystal display panel having a good adhesion to the substrate and also to the production method of such a liquid crystal display panel.

Figure 1 illustrates the construction of a atypical conventional liquid crystal display panel. Figure 1 (a) is a plane view and Figure 1 (b) is a sectional view taken along the line A-A' of Figure 1(a).

In the drawings, reference numerals 1 a and 1 b represent substrates of polyester films as organic polymer films and reference numerals 2a and 2b represent electrodes of transparent conductive membranes such as In203, SnO2 or the like that are disposed on the adjacent surfaces of the substrates Aa and ib. Reference numeral 3 represents electrode terminals used for connecting the electrodes 2a, 2b to an external circuit and reference numeral 4 represents an oriented film. Reference numeral 5 represents an epoxy-type adhesive material for bonding the peripheries of the substrates la, 1b together, and reference numeral 6 represents a liquid crystal seaied between the substrates la and ib.

The organic polymer film must have high resistance to the liquid crystal because the latter has a strong polarity.

If the substrates la, 1b consist of organic polymer films, stress concentrations occur in them because they are flexible. Accordingly, the peripheries of the substrate 1 a, Ib must be firmly bonded The following two methods are heretofore known as bonding methods: (1) a method which partially dissolves the bonding surfaces of the organic polymer film using a solvent; and (2) A bonding method which uses an epoxy type adhesive such as shown in Figure 1.

However, these bonding methods have the drawback that the bonding strength is low.

As disclosed in U.S. Patent No. 2,764,502, for example, it is known that the bonding strength can be generally improved by first subjecting the bonding surfaces of the organic polymer films to a surface treatment with NaOH or the like, and then bonding the films by the use of an adhesive. Though this method certainly improves the bonding strength, it is not free from problems such that the surface becomes cloudy and turbid and loses its transparency, and the surface quality drops.

The present invention is therefore directed to provide a liquid crystal display panel which eliminates all the above problems with the prior art and improves the bonding strength of substrates consisting of organic polymer films without sacrificing any transparency. The invention relates also to a production method of such a liquid crystal display panel.

In a liquid crystal panel of the type in which a liquid crystal is sealed between substrates consist ing of a pair of organic polymer films, transparent conductive layers are disposed on the adjacent surfaces of the organic polymer films and the peripheries are bonded by an adhesive, the characterizing features of the present invention accom plishing the object described above reside in that a chemical treatment with a strong alkali or acid is applied to at least the adjacent surfaces of the organic polymer films, and organic polymer layers are deposited over the display areas on the adjacent surfaces of the substrates.

The present invention is based upon the following experimental data discovered by the inventors of the present invention.

A 100 ,um thick polyester film was dipped into an aqueous NaOH solution having an arbitary concentration and temperature for an arbitary period of time and was thereafter washed with water for about 5 minutes. The film was then dipped into a 1% aqueous stannous chloride solution for about 5 seconds, was washed sufficiently with water and thereafter dried.

Two polyester films chemically treated in this manner were bonded to each other by a polyester adhesive and then heat-cured at 12G C for a short period of time. The bonding strength was measured in accordance with the T peeling strength of the JIS (Japan Industry Standards). The results are shown in Figures 2 through 4. Each diagram shows the strength relative to a T peeling strength which is set to 1 when no chemical treatment is applied. Symbols x represent the breakage of a polyester film.

Figure 2 shows the relationship between the treatment temperature and the T peeling strength when the treatment was carried out for one minute using a 20% by weight aqueous NaOH solution. It can be seen that the higher the treatment temperature is, the higher the bonding strength becomes.

Figure 3 shows the relationship between the concentration of the aqueous NaOH solution and the T peeling strength when the treatment was carried out at 80"C for one minute. It can be seen that the higher the concentration of the aqueous NaOH solution is, the higher the bonding strength becomes.

Figure 4 shows the relationship between the treatment time and the T peeling strength when the treatment was carried out at 80oC using a 20% by weight aqueous NaOH solution. It can be seen that the longer the treatment time is, the higher the bonding strength becomes.

It can be appreciated from Figures 2 through 4that a concentration of the aqueous NaOH solution ranging from 10 to 20% by weight, a treatment temperature of 60 to 80"C and a treatment time of about 1 minutes are preferable as practical ranges.

Besides NaOH as the chemical treatment agent for the polyester film, strong alkalis such as KOH and LiOH and oxidants such as dichromic acid provide substantially the same effect. As well as polyester adhesive, epoxy resin adhesives provide the same effect.

These results may be attributed to the fact that the surface of the polyester film, which is otherwise stable, is activated by the chemical treatment.

However, a chemical treatment forms fine de pressions on the surface of the polyester film and hence the surface becomes cloudy, thereby reducing the light transmittance of the film. However, this phenomenon does not occur uniformly over the entire film surface being chemically treated, and when the film is locally examined, shadows can be seen as if spots are formed. Accordingly, the quality of a display panel is reduced.

The inventors of this invention have determined that when an organic polymer layer preferably having a thickness of up to 1 m is coated and cured onto the chemically treated surface in order to prevent the polyester film from becoming cloudy, cloudiness in the film as well as any drop in light transmittance can be prevented.

Figure 5 is a diagram showing the relationship between the treatment time versus the light transmittance and the cloudiness when the treatment is carried out at 800C using a 20% by weight aqueous NaOH solution. In the diagram, the solid line a and the dashed line b represent the light transmittance and cloudiness of the polyester film as treated chemically under the conditions described above, while the solid line a' and the dashed line b' represent those of a polyester film which is first treated under the same conditions as described above and then is dried at 1200C for several minutes after a 10% polyamide resin dissolved in a solvent is uniformly sprayed onto the chemically treated surface by a spray method.According to this diagram, the cloudiness and deterioration in light transmittance can be prevented by depositing an extremely thin layer of polyamide resin which is the organic polymer, on the chemically treated surface of the polyester film.

It has also been found that even after an organic polymer layer is deposited extremely thinly on the chemically treated surface of the polyester film, the bonding strength hardly deteriorates. This is presumably because the organic polymer layer is extremely thin and a large number of pin-holes exist in the layer, and the adhesive penetrates into these pin-holes.

Besides the polyamine resin, it is also possible to use polyimides, polyacryinitrile, polyvinyl alcohol and the like as the organic polymer layer. Preferably, the organic polymer layer will have a refractive index approximately equal to that of the polymer film, such as the polyester film (about 1.65) used as the substrate and it has been found that if the difference of these refractive indices is within +20%, the objects of the present invention can be sufficiently accomplished.

The above and other objects and features of the present invention will become more apparent from the description of some preferred embodiments thereof.

Figure 1 is a plane and sectional view of a liquid crystal display panel in accordance with prior art; Figures 2 through 5 are diagrams useful for explaining the principle and effect of the present invention; Figures 6 through 11 are sectional views of the first embodiment of the present invention with Figure t2 being its plane view; Figures 13 and 14 are sectional and plane views of the second embodiment of the present invention, respectively; Figure 15 is a sectional view of the third embodiment ofthe present invention; Figure 16 through 20 are sectional views of the fourth embodiment of the present invention; Figure 21 and 22 are sectional views of the fifth embodiment of the present invention; and Figure 23 is a plane view of the sixth embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to some preferred embodiments thereof.

The first embodiment of the present invention will be described with reference to Figures 6 through 12.

A polyethylene film 9 is bonded to one of the main surfaces of a 100 ssm thick polyester film 7 by a polyester adhesive 8 to form a substrate 10 (Fig. 6).

The polyethylene film 9 is chemically stable and is used to protect the non-bonded surface of the polyester film 7. However, this film 9 is not always necessary. The cloudiness would become large and light transmittance of the polyester film 7 would deteriorate if the polyethylene film 9 were not bonded, because both main surfaces of the polyester film 7 are treated chemically. After the chemical treatment is carried out, the polyethylene film 9 may be removed, if desired.

Next, the substrate 10 is dipped into a 20% by weight aqueous NaOH solution kept at 80%C for about one minute, is then washed with water for about 5 minutes and is dipped into a 1% aqueous stannous chloride solution for about 5 seconds, followed by washing with water again. Fine depressions 11 are formed on the main surface of the polyester film 7 which is not protected by the polyethylene film 9 (Fig. 7).

A transparent conductive layer 12 of ln203, SnO2 or the like, having a thickness of 400 to 500 , is deposited on the chemically treated surface in accordance with a known process (Fig. 8).

This transparent conductive layer 12 is etched by a known photoetching process to obtain a transparent conductive layer 13 having any desired pattern (Fig.

9).

Thereafter, an 800 to 1000 Thick polyamide film 16 is formed, by a printing method to prevent cloudiness tFig. 10). The surface of the polyamide film 16 is rubbed with a cloth. Here, the polyamide film 16, which is the organic polymer layer, serves also as an orientation controlling film having the function of orienting the liquid crystal molecules in a specific direction. It is also possible to accomplish the objects of the present invention by further reducing the thickness of the polyamide film 16 preventing cloudiness, then disposing another known polyamide type of film thereon and rubbing the surface of the latter to form the orientation controlling film.

Next, after the polyethylene film 9 is peeled off, two substrates 10a and lOb are superposed via inorganic spacers 17 in such an arrangement that the main surfaces that have the transparent conduc tive layers 13 face each other with an approximately 10 ,zm gap between them. The peripheries of the substrates 10a, 10b are bonded with a polyester or epoxy resin adhesive 18. A sealing port 19 is disposed on one of the sides from which the electrode terminals 14 do not extend. After a liquid crystal 20 is inserted via this sealing port 19, the port 9 its thermally fused, completing the liquid crystal display [Fig. 11 (sectional view) and Fig. 12 (plane viewil.

In His embodiment, since the chemical treatment is applied to the bonding surfaces of the polyester fi'm, the bonding strength of the substrates is further Increased. Since the polyamide film 16 as the organic polymer layer is disposed on the chemically treated surface, the substrates do not lose any t?aflbparnncy.

Moreover, the production steps can be reduced because the polyamide fiim 16 serves also as the orientation controlling film.

Next, the second embodiment of the present invention will be described with reference to Figures 13 and 14.

ln this embodiment, the steps corresponding to those of the first embodiment shown in Figures 6 through 9 are the same and are therefore omitted from this description.

In Figure 13 showing this embodiment, the polyamidefilm 16 is not formed over the bonding areas of the substrate 10 but the polyester films 7a, 7b are bonded directly by an adhesive 18 as shown in Figure 14. The subsequent steps are the same as those of the first embodiment and are omitted from this description.

According to this embodiment, since the polyamidefllm 16 is not formed over the bonding areas 10a, 10b of the substrates, the bonding strength can be further improved.

Next, the third embodiment of the present invention will be described with reference to Figure 15.

Two 100 sm thick unidirectionally stretched polyester films 71, 72 and a 50 ,mm thick polarizer 30 formed by placing a dichromic pigment (iodine, methyl red, etc.) in PVA are laminated using a polyester adhesive, forming the substrate 10 as a composite film.

This embodiment is the same as the second embodiment except that the structure of the substrate 10 is different from that of the second embodiment.

According to this embodiment, since the substrate serves also as a polarizer, the thickness of the liquid crystal display can be further reduced and the display quality can be improved, in addition to the effects brought forth by the first and second embodiments.

The fourth embodiment of the present invention will be described with reference to Figures 16 through 20.

In this embodiment, the steps corresponding to those of the first embodiment shown in Figures 6 and 7 are the same and are therefore omitted from this description.

In Figure 16, a polyamide resin diluted by a solvent is sprayed onto the chemically treated surface of the substrate 10 and is dired at 1 20"C for 20 minutes to form a 0.5 ,a thick polyamide film 16.

Thereafter, a 400 Ato 500 thick Athicktransparent conductive layer 12 of ln203, SnO2 or the like is formed on the polyamide film 16 by a known method (Fig. 17).

This transparent conductive layer 12 is then etched by a known photoetching technique to obtain a transparent conductive layer 13 having any desired pattern (Fig. 18).

An 800 to 100 thick polyamide orientation film 22 is further formed on the electrode-forming surface bye printing method (Fig. 19).

After the polyethylene film 9 is peeled off, the two substrates 1 ova, 1 Ob are superposed via inorganic spacers 17 so that the main surfaces on which the transparent conductive layers 13 are disposed face one another with a gap of approximately 10 ym between them. The peripheral areas of the substrates 10a, lOb are then bonded using a polyester or epoxy resin adhesive 18. A sealing port 19 is disposed on one of the sides of the substrates 1 Oa, lOb from which electrode terminals 14 do not extend, and a liquid crystal 20 is inserted via the port 19. The sealing port 19 is heat-fused to seal it, completing the liquid crystal display 21 (Fig. 20).

This embodiment also provides the same effects as those of the first embodiment.

The fifth embodiment of the present invention will be described with reference to Figures 21 and 22.

In Figure 21 of this embodiment, the polyamide film 16 are not formed over the bonding area of the substrates but the polyester films 7a and 7b are bonded directly using a polyester adhesive as shown in Figure 22. The subsequent steps are the same as those of the fourth embodiment and are therefore omitted from this description.

Since the polyamide films 16 are notformedover the bonding areas of the substrates 10a, 1Ob in this embodiment, the bonding strength can be further improved.

In the foregoing embodiments of the invention, only the sealing port 19 for the liquid crystal is heat-fused to seal it as depicted in Figure 12. In this embodiment, however, the periphery of the sides 211 from which the electrode terminals of the polyester films 7 are to extend are bonded by a polyester or epoxy resin adhesive 18 as shown in Figure 23 and after the liquid crystal 20 is inserted via the two sides 212 that have no terminals, the sealing port is heat-fused to seal it.

In the foregoing embodiments of the present invention, a polyester film 7 is used as the polymer film by way of example, but the present invention can use any of those polymer films which have a low bonding strength with respect to the adhesive.

Besides polyamide resin, polyimides, polyacrylonitrile, polyvinyl alcohol and the like can be used suitably as the organic polymer layer, as described already. If the organic polymer layer also functions as the orientation controlling film, the practical range of the thickness of the polymer layer is about twice that of the transparent conductive layer 13.

As described in detail in the foregoing, the present invention provides a liquid crystal display panel having an improved bonding strength of the substrates without sacrificing any transparency in liquid crystal display panels using a polymer film as the substrates, and also a production method of such a liquid crystal display panel.

Claims

1. A liquid crystal display panel having a liquid crystal supported between a pairofsubstrates consisting of polymer films each equipped with at least one transparent conductive film over a display area on the adjacent surface thereof with respect to the other and the peripheral areas of said pair of substrates bonded together by an adhesive, wherein at least the adjacent surface of at least one of said polymer films has been subjected to chemical treatment by a strong alkali or acid and an organic polymer layer has been deposited over the display area on the adjacent surface of said substrate.

2. A display panel according to claim 1 wherein said organic polymer layer has been subjected to an orientation treatment.

3. A display panel according to claim 1 or 2 wherein the refractive index of said organic polymer layer is from 80% to 120% that of said polymer film.

4. A display panel according to any one of the preceding claims, wherein the thickness of said organic polymer layer is approximately twice that of said transparent conductive layer.

5. A display panel according to any one of preceding claims wherein said polymer film is a polyester film.

6. A display panel according to claim 1 substantially as hereinbefore described with reference to any one of Figures 6-23 ofthe accompanying drawings.

7. A method of producing a liquid crystal display panel which comprises: subjecting at least one main surface of a polymer film to chemical treatment with a strong alkali or acid; disposing at least one transparent conductive layer over said one main surface; depositing an organic polymer layer over said one main surface on which said transparent conductive layer is deposited to form a substrate; bonding the peripheral areas of a pair of such substrates with an adhesive so that said one main surface of said substrate faces that of the other substrate with a predetermined gap between them; and sealing a liquid crystal into said predetermined gap.

8. A method according to claim 7 wherein, after said organic polymer layer is deposited, said organic polymer layer is oriented.

9. A method of producing a liquid crystal display panel which comprises: subjecting at least one of the main surfaces of a polymer film to a chemical treatment with a strong alkali or acid; depositing an organic polymer layer on said one main surface; disposing at least one transparent conductive layer on said one main surface; depositing an orientation film on said one main surface, thereby forming a substrate; bonding the peripheral area of a pair of such substrates with an adhesive so that said one main surface of said substrate faces that of the other substrate with a predetermined gap between them; and sealing a liquid crystal into said predetermined gap.

10. A method according to any one of claims 7-9 wherein said chemical treatment with said strong alkali or acid is a chemical treatment using an aqueous NaOH solution having a concentration of 10 to 20% byweight, thetreatmenttemperature isat 60-80"C and the treatment time is approximately one minute.

11. A method according to any one of claims 7-10 wherein a polyethylene film is deposited on the other main surface of said polymer film and, after chemical treatment with strong alkali or acid is applied, said polymer film is removed.

12. A method according to any one of claims 7-11 wherein said polymer film is a polyester film.

13. A method according to claim 7 and 9 substantially as hereinbefore described with reference to any one of Figures 6-23 of the accompanying drawings.